Example, for a 10 tooth driver, 88 tooth driven
and
a 34.5 in. roll out – OR = 39.37 x 88 / 10 / 34.5 =10.04 rev/meter
Note that the higher the ratio is its numerical value is lower and
vice versa.
When trying a different gear ratio you want to
evaluate
its result on your performance. The stopwatch may tell the story, but
you
also probably want to know how your top speed was affected. If you use
a tachometer with a maximum recall you can use this to calculate your
top
speed. The formula for speed is:
V (km/h) = RPM x Driver teeth x Roll out / Driven teeth / 656.2
So for the above example at 15000 rpm the speed is – V = 15000 x 10 x 34.5 / 88 / 656.2 = 89.6 km/h.
As a general rule I believe its best to find the
lowest ratio that does not cause a loss of top speed or over revving of
your engine, as this will give the best jump out of the slow corners.
Don't
ignore the stopwatch either. For quick reference I like to use a chart
that shows the overall ratio and maximum speed for the typical ratios
you
would use and your typical maximum RPM. This can be done manually or on
a spreadsheet program. I limit my charts to the gears I have in my
toolbox
and sort it by overall ratio. Here is a sample you can expand on.
| Overall Gear Ratio Chart |
Speeds
shown are km/h
at -
|
|
RPM | ||||||||
| Roll out-> | 33.75 | 34.00 | 34.25 | 34.50 | 34.75 | ||||||
| Driver | Driven | OR | Speed | OR | Speed | OR | Speed | OR | Speed | OR | Speed |
| 13 | 64 | 5.74 | 66.87 | 5.70 | 67.36 | 5.66 | 67.86 | 5.62 | 68.35 | 5.58 | 68.85 |
| 13 | 62 | 5.56 | 69.02 | 5.52 | 69.53 | 5.48 | 70.05 | 5.44 | 70.56 | 5.40 | 71.07 |
| 13 | 60 | 5.38 | 71.32 | 5.34 | 71.85 | 5.31 | 72.38 | 5.27 | 72.91 | 5.23 | 73.44 |
| 14 | 64 | 5.33 | 72.01 | 5.29 | 72.54 | 5.25 | 73.08 | 5.22 | 73.61 | 5.18 | 74.14 |
| 13 | 58 | 5.20 | 73.78 | 5.17 | 74.33 | 5.13 | 74.88 | 5.09 | 75.42 | 5.05 | 75.97 |
| 14 | 62 | 5.17 | 74.33 | 5.13 | 74.88 | 5.09 | 75.43 | 5.05 | 75.98 | 5.02 | 76.53 |
| 13 | 56 | 5.03 | 76.42 | 4.99 | 76.98 | 4.95 | 77.55 | 4.92 | 78.12 | 4.88 | 78.68 |
| 14 | 60 | 5.00 | 76.81 | 4.96 | 77.38 | 4.93 | 77.95 | 4.89 | 78.52 | 4.86 | 79.09 |
| 15 | 64 | 4.98 | 77.15 | 4.94 | 77.72 | 4.90 | 78.30 | 4.87 | 78.87 | 4.83 | 79.44 |
| 14 | 58 | 4.83 | 79.46 | 4.80 | 80.05 | 4.76 | 80.64 | 4.73 | 81.22 | 4.69 | 81.81 |
| 15 | 62 | 4.82 | 79.64 | 4.79 | 80.23 | 4.75 | 80.82 | 4.72 | 81.41 | 4.68 | 82.00 |
| 14 | 56 | 4.67 | 82.30 | 4.63 | 82.91 | 4.60 | 83.52 | 4.56 | 84.12 | 4.53 | 84.73 |
| 15 | 60 | 4.67 | 82.30 | 4.63 | 82.91 | 4.60 | 83.52 | 4.56 | 84.12 | 4.53 | 84.73 |
| 15 | 58 | 4.51 | 85.13 | 4.48 | 85.76 | 4.44 | 86.40 | 4.41 | 87.03 | 4.38 | 87.66 |
| 15 | 56 | 4.36 | 88.17 | 4.32 | 88.83 | 4.29 | 89.48 | 4.26 | 90.13 | 4.23 | 90.79 |
Changing valve
springs
at the track
Or anywhere else for that matter. Although I have
never seen a valve spring break, they do start to take a permanent set
(collapse) pretty quick. So we put fresh springs in every 2 or 3 races.
The springs are pretty cheap (about $3 each) and easy to change without
removing the head. So it is good insurance to change them often.
Here's the way I do it. Remove the valve cover and
spark plug, then turn the engine over until the piston is at top dead
center
on the compression stroke (Both valves are closed). I use a screwdriver
in the spark plug hole to feel the piston at top position. With a
screwdriver
in one hand, push the valve spring keeper down enough to turn the
rocker
arm to one side of the valve with the other hand, thus exposing the
spring
keeper. Remove the valve rotator "pill" from the exhaust valve stem.
Unpack
the new springs and have them sitting upright within reach, ready to
use.
Fish the bent end of an "L" shaped Allen Key into the spark plug hole
and
position it so that it holds the valve closed by levering it against
the
piston top with light force (don't force piston down). While holding
the
valve shut with the Allen Key in one hand use the other hand to remove
the valve spring keeper and spring, install the new spring and
re-engage
the spring keeper. Replace the exhaust valve "pill". Press the spring
keepers
down as before and engage the rocker arms. Check and adjust the valve
lash.
It should not have changed, as we did not touch the adjuster nuts. This
process only takes 5 minutes, but don't rush it, and don't be
interrupted
while you are doing it. You don't want to drop the valve into the
cylinder.
Note that the two spring keepers are different, as only one accepts the
exhaust rotator pill, so don't mix them up. If you accidentally drop a
valve, it may still be engaged in the valve guide. You can usually fish
it back up with the Allen Key or by carefully raising the piston if it
has gone down a bit. Otherwise you have to remove the head to recover
the
valve (very rare).
top of page
Race prep your Clone engine Note: Also see Affordable Go Karts web site for similar "how to" descriptions to these here.
To get a race prepared Honda you've got a few
options.
You can buy a new race ready engine form one of the several engine
builders
in your area (in the Vancouver area I suggest Red Head or Bulldog. You
can buy a used motor from another racer. If you buy a used motor, you
should
go through it or have it freshened up before it is run. Or you can buy
a new Honda and do the race prep yourself. This is the route we took.
It
saved us some money, but the greatest reward is when you beat some of
the
pro-built engines. I'll go through what you should do to get going with
a Honda GX200 (6.5 hp) or GX160K1 (5.5 hp) engine.
Start with a copy of the ASN Canada rule book and
a repair manual that covers these engines (Haynes Small Engine Repair
is
fine). The modifications that we will make to the engine are as
follows.
For
the majority of clone engines I have worked on a #82 main jet is a good
choice. I would start here and go up or down 1 sixe at a time to find
your best jetting. This is the only change made to the carb metering. I
am using the stock clone emulsion tube in this case as our rules
stipulate. If your rules allow different emulsion tubes then the jet
size will change as well. Rather than buy Honda jets I usually just
drill out the stock jet with a "Number Drill Set". For #82 jet
size I use a #67 (0.032") drill. When drilling jets, I hold the drill
bit in a pair of pliers and turn the jet with my fingers against the
drill. Drill the jet out one drill size at a time in multiple steps. Do
not try and use a drill motor as you are lible to go oversize and ruin
the jet. The "engine build report" mentioned at the bottom of this page has a #drill size to jet size cross over table.
Install a pulse driven fuel pump. The main object here is to minimize the opportunity to get oil transferring from the crankcase through the pulse tube to the pump diaphragm. If the pump diaphragm cavity fills with oil it will impede the pumps operation. I installed my fitting in the case side cover just behind the top rear bolt. Locate the hole so that it is inside and clear of the internal rib structure of the cover. Drill and tap the cover for a 1/8" NPT fitting. Install a 1/8 npt to 1/4" barb fitting with thread sealant in the hole. Mount the pump over the engine and connect the pulse hose between the engine and pump. The pump and hose should be arranged so that any oil in the line will drain back to the crankcase. Install a small fuel filter in the line from the tank to the fuel pump. I also mount a squeeze bulb primer pump in the line from the tank, which makes it easier to start the engine if the carb was dry. Keeping the fuel cool is a good idea, so consider incorporating an insulator in the pump mounting.
Lap the valves and set valve lash. Just
like piston ring seal, valve sealing is soooo important to top
performance.
Hand lap the valves with a fine lapping compound, followed by a fine
metal
polishing compound.
Valve lash also plays a role in how your engine
will respond. Generally speaking we are looking for a tight lash
setting
to increase valve lift and open duration. A good place to start is
0.002"
cold for both intake and exhaust. When the engine is hot the cylinder
and
barrel, being aluminium, will grow more than the valve linkage,
resulting
in a looser setting. If you set the lash to tight when the engine is
hot,
then there may be no clearance when it is cold. A tight setting will
benefit
power at high rpm while a looser setting will be better at lower rpm
and
produce more torque when exiting corners. Because we have no gearbox
the
engine must produce good power across a wide range of rpm. What's best
at high rpm and peak output may not be the hot ticket overall if it
takes
too much away in the midrange.
A couple of pointers for adjusting valve lash. First
loosen and re-snub the adjuster jam nuts just so that the adjuster can
still be turned with moderate effort, similar to the effort of turning
a stover lock nut. Then adjust the valve lash by turning the adjuster
nut
(the jam nut should follow). Done. No need to tighten the jam nut
further.
Next time you do an adjustment, all you have to do is turn the adjuster
nut. The jam nut only needs to be tended to if the adjuster turning
effort
is too light. Do not set the valve lash with the jam nut loose, as when
you tighten it, it will shift the backlash in the adjuster threads and
throw your setting off.
Altering the cam timing.
Advancing
or retarding the cam timing will have an effect on the power curve and
where on the curve power is maximized. In considering the timing of
four
events, intake opening, intake closing, exhaust opening and exhaust
closing,
it is generally accepted that the point at which the intake valve
closes
has the most effect on performance. By the time the intake valve closes
the piston has completed its downward travel and is beginning to come
back
up on the compression cycle. even though the piston is moving upward,
the
inlet air/fuel charge is continuing to flow into the cylinder due to
the
flow inertia, or ram effect. As the piston moves up, pressure increases
in the cylinder. At the point where this pressure equals the ram
pressure,
intake flow reversion begins to occur. Having the intake valve open
beyond
this point of reversion is just wasteful and hurts compression and
cylinder
filling, thus causing a loss of power. Conversely if the intake valve
closes
before he reversion point then a lost opportunity to completely fill
the
cylinder with air and fuel is realized, and power is not optimized. The
problem is that the reversion point varies with engine speed. At higher
rpm the piston is further up on the compression stroke before reversion
occurs. For this reason a retarded cam will work better at high rpm
while
advancing the cam will produce more torque at low rpm. As we are
dealing
with Honda GX160K1 and GX200 engines here, and they each have quite
different
cam profiles, my recommendations are specific to our experience with
each
engine. On the GX160K1 we have had good results by retarding the timing
4 degrees from the stock position. This is for an engine that is
running
without any restrictor plate. We have not run with a restrictor, but my
guess is that the restrictor would hurt the ram effect and advance the
reversion point, so I suspect he stock cam timing would work better. On
the GX200 the cam profile has a much later intake closing event than he
GX160 so we have been happy with leaving the cam timing as delivered
from
Honda.
The
cam drive gear is simply a press fit on the crankshaft, so to retard
the
timing it is removed, turned 4 degrees clockwise (viewed from the drive
end) and pressed back on. Sounds simple, but how do you know if it has
been moved the correct amount? First we must take a reading of the
cam's
initial position. Install and zero your degree wheel. Rig up a dial
indicator
with an extension that extends down the intake pushrod hole and bears
on
the valve lifter. With the degree wheel at TDC on the compression
stroke,
zero the dial indicator reading. The dial indicator reading is set to
zero,
but the pushrod should still have some extension travel available. Turn
the flywheel clockwise (viewed from the flywheel end) until the dial
indicator
reading is descending to 0.020" and record the degree wheel reading at
this point. This reading should be close to 215 degrees ATDC. Note,
always
turn the flywheel clockwise for these readings to avoid any errors
caused
by backlash in the cam gears. If you don't have a dial indicator then
you
can get by with a feeler gauge. In this case, first set the valve lash
at 0.025" at TDC. Then using a 0.005" feeler turn the flywheel just
until
the rocker pinches the feeler (0.020" before valve close) and record
the
reading on the wheel. Repeat several times to ensure repeatability of
the
reading. Scribe alignment marks on the crank gear and the crankshaft
for
visual reference when re-setting the gear. Scribe a second mark on the
crank about 0.040" to the right of the first. Using a gear puller, pull
the gear and stop pulling just short of releasing it from the shaft.
Now
scribe alignment marks on the back side of the gear and the shaft.
These
marks are easier to reference when starting the gear back on the shaft.
Now remove the gear, rotate it the 0.040" or 4 degrees clockwise and
press
it back on. To press it back on I use a piece of 5/16 UNF treaded rod
in
the end of the crank, a short piece of tubing or pipe, a washer plate
and
a nut. Warming the gear helps too. Re-install and zero the degree wheel
and re-check the reading at 0.020" before intake closing as done
before.
The new reading should be about 219 degrees ATDC if you were lucky. If
the reading is not what you expected then you can decide to fix it or
try
it on the track. It's your call.
I don't have a gear puller, so I made up a Mickey
Mouse puller that works fine. I used three 3/8" carriage bolts with
their
heads hooked over the gear, a plate over the end of the crank drilled
for
the three bolts, and a hose clamp to hold the bolts against the gear.
Progressively
tighten the bolts to pull the gear off.
Another way to do this is to turn the gear on the
crank, rather than pull it off and push it back on. I haven't tried
this
yet but you would wrap a strip of lead about 3/8" thick around the gear
then use a big pipe wrench to turn it. The lead is to protect the gear
teeth from damage and give the wrench traction.
Raise
compression
ratio by decking the block. To play this game you will need a 50
cc
burette to measure the combustion chamber volume. Check
your rules to see what the minimum combustion chamber volume is allowed
and if you even allowed to make this modification. 
The
measuring procedure is described in the ASN Canada rule book under
section
36.2 of the Technical Regulations. To avoid being disqualified, you must leave a little room for
carbon
build up. I suggest making these adjustments after you have run the
engine
for 2 or 3 races to build up some carbon. You can then measure the
volume
with carbon and after cleaning it out to determining how much allowance
is needed. For reference, each 0.10 cc volume reduction requires a
0.0011"
deck cut on the block.
To shave the deck I use a piece of 1/2" thick plate
glass with a sheet of sandpaper taped to it. I tape the glass down to
my
work bench and completely strip the block. Then I sand the deck down by
working it in a figure eight pattern on the sandpaper. I start with 320
grit and finnish with 600 grit. I measure progress with a depth gauge
in
the head bolt holes. Proceed slowly and check your progress carefully,
as going too far is a disaster. So far the Clone engines that I have checked
don't
need much cut, so even if you don't do this it probably won't make much
difference. I am currently running an engine that is not decked, and it is
competitive.
Modify the throttle linkage. A
couple of points to consider here. Whatever you use for throttle
linkage,
you want to make sure that it won't damage the carburettor throttle
lever
or butterfly shaft with linkage over travel. If these parts are
damaged,
they are not listed separately as service parts by Honda and would
require
carb replacement or an alternative repair. And secondly make sure you
have
adequate return springs in the system. I use 3 return springs, one
directly
on the butterfly shaft lever, one on the relay lever on the engine, and
one on the accelerator pedal. My linkage system uses a relay lever that
is mounted on a pivot bolt that is threaded into the governor shaft
hole
on top of the case. 
From
this lever I use a pushrod made from a bicycle wheel spoke to actuate
the
carb throttle lever. I have a bend in this pushrod so that when the
carb
lever reaches its stop the pushrod will bend, or buckle, and not put
excessive
force on the carb lever. The pushrod is such that it returns to its
normal
shape when the accelerator is released. The relay lever also reverses
the
direction of travel so that the accelerator cable can extend forward
directly
towards the pedal. In my layout I mount the accelerator cable to one of
the front fuel tank ears. Another method of achieving over travel
safety,
is to insert a tension spring between the cable end and the lever or
pedal.
For a throttle cable, I use a bicycle long shifter cable (the light
variety)
which I buy without a sheath. For a cable sheath I use 3/16" nylon
tubing
with compression fittings for end attachments. The cable is quite loose
in the tubing and doesn't bind. To mount the sheath to the motor I
drill
and tap the front of the fuel tank mount ear 1/8" NPT for the
compression
fitting.
Install Header and Muffler.
Firstly you can build your own header, as I do, if you have a MIG
welder.
I have a local fab shop hi-defenition plasma cut the flange plate and pre bend the
tube.
I use 1" OD x 0.058" wall 4130 (chrome molly) aircraft tube. This tube
is a bit tricky to bend without buckling, but if you use a large radius
and limit the bend angle it will turn out fine. Do not try bending it
without
a good tube bender. To have flanges cut you can download the following
CAD and Acrobat files. The fab shop can use the CAD file to program
their
cutting machine.
FLANGE CAD FILE (.dxf)
FLANGE ACROBAT FILE (.pdf)
Note that my flange has a round hole and needs to be "port matched" to
the head by grinding or filing as described in the ASN Canada Honda
rules. You also need to weld a pipe nipple (cut in half) to the
end along with a support and locking tab for mounting the muffler.
You can also purchase ready made headers from kart suppliers. The British Columbia Clone rules require that the header meets the ASN Canada Honda header rules, so the RLV5436C does among others. Basically it must be 1" OD for its entire length of 12" maximum. You will the need to weld a 1" nipple to the end, as described above, if you are using the industrial muffler option.
Install air filter and filter adapter. Rules affecting air filters and air filter adapters have changed periodically. Make sure you understand the current rules and use components that meet them. There may be some parts, new or used, out there that do not conform to the current rules and should be avoided.
Install clutch. My comments
here
apply to the "Max Torque SS" type of clutch, but may also
apply
to other brands as well. The clutch may be installed with the drive
sprocket
inboard or outboard, whichever way works best for your situation. The
clutch
is retained with a 5/16 UNF bolt and flatwasher in the end of the
crankshaft.
When installed the clutch will have some "end play" on the crankshaft
and
can float in and out. This is OK. I tried clamping the clutch tight
with
no end play, my fist time, and only damaged the clutch drive hub. Your
clutch should be serviced after each race. I clean and de-glaze the
drum
and shoes, and clean and re-oil the bushing with two drops of oil. Do
not
over oil the bushing as it will bleed onto the shoes and prevent
lockup.
Note that if you are governed by the British Columbia Clone rules it
requires a Max Torque SS clutch and not a Max Torque Stock Clone clutch.
| Parts required to build and install a Honda GX200 engine. | |||
| Part number | Quantity | Description | Sources |
| NPN | 1 | 6.5 HP Clone engine | Princess Auto 8088379 |
| 99101-ZF50820 | 1 | #82 main jet. | Penticton Honda |
| 16166-ZE1-005 | 1 | GX140 emulsion tube (nozzle) | Penticton Honda |
| 06111-ZL0-000 | 1 | Engine gasket kit (all). | Penticton Honda |
| 12391-ZE1-000 | 0 | Valve cover gasket | Penticton Honda |
| 12251-ZL0-003 | 0 | Head Gasket (shim style) | Penticton Honda |
| 11381-ZB2-800 | 0 | Crankcase side cover gasket | Penticton Honda |
| 18381-ZH8-800 | 0 | Exhaust header gasket | Penticton Honda |
| 13331-357-000 | 0 | Flywheel key (file to advance ignition timing). | Penticton Honda |
| 13011-ZL0-000 | 0 | Piston ring set, standard size | Penticton Honda |
| 14751-883-000 | 2 | Valve spring, G200 | Penticton Honda |
| BPR6ES | 1 | NKG spark plug. | Auto Supply |
| 1 | Pulse fuel pump | Kart shop or ? | |
| 16700-ZL8-013 | or | Fuel pump from a Honda GC160 | Penticton Honda |
| 325-4A or 125-4A | 1 | 1/8 npt to 1/4" barb fitting (pump pulse) | Industrial Supply |
| 1 |
Industrial Muffler
(Atlas
AT-0071) |
Canadian Tire 60-7087-8 ($7.50) |
|
| 1 |
Industrial Muffler (Kohler 275679) | Princess Auto 8197725 ($6) |
|
| 1 | RLV-B91-1" muffler | Kart Shop | |
| 1 | Honda 1" x 12" header pipe. | Kart Shop RLV5438C | |
| 1 | 1/8 x 3/4 steel flatbar 16" long for muffler brace. | ||
| 1 | Pipe nipple, 1" steel, cut in half and welded to header for muffler mounting | Plumbing supply | |
| 10 | Header wrap tape 1" wide. | Auto Supply | |
| 1 | Air filter adapter | Kart shop | |
| 1 | Air filter | Kart Shop | |
| 1 | Engine mounted chain guard. | Kart Shop | |
| 1 | Max Torque SS clutch with 14 tooth #35 driver. SS1434 | Kart Shop | |
| 1 | 62 tooth #35 split rear sprocket.(plus other sizes as required) | Kart Shop | |
| 1 | #35 chain, 36" long | Industrial Supply | |
| 1 | "Rust Check" spray Chain lube) | Canadian Tire | |
| 1 ft. | 3/16" fuel hose (yellow that stays soft) | Penticton Honda | |
| 5 ft. | 1/4" fuel hose (yellow that stays soft). | Penticton Honda | |
| 1 | Fuel primer bulb, 1/4" | Canadian Tire | |
| 2 l | 5-50w non synthetic oil (14oz / 450ml per fill) for break-in | ||
| 2 l | 5-50w full synthetic oil (14oz / 450ml per fill) after break-in. | ||
| 1 | 5-30w motor oil for break in only then switch to synthetic | Canadian Tire | |
| 1 | Throttle cable (lightest bicycle shifter cable) | Bicycle store | |
| 1 | Throttle cable sheath, loose fit.(bicicle brake cable sheath or 3/16" nylon tubing) | Bicycle store or Industrial Supply | |
| 2 | Cable sheath end compression fitting, 68-3A (1/8" NPT to 3/16 tube) | Industrial Supply | |
| GX 10 000 000 | 1 | Throttle cable end spud | Penticton Honda |
| 1 | Motor mount, 4 cycle | Kart Shop | |
Need a Degree Wheel? Make your own. Just download my degree wheel drawing, print it off on as large a sheet of paper as you can, cut it out and glue it to a piece of aluminium or masonite. Drill the center for your 5/16 clutch bolt, and your done. Make up a pointer that bolts to the fuel tank ear on the block and file or grind a chisel point on it. The larger your degree wheel is the easier it is to get accurate readings.
Download my "Engine build report" sheet Build Report.
Here's a handy chassis setup and timing record sheet that we use.
Some other links:
Do it
yourself
karting - Jamie Webb's self help site has lots of good tech
info.
top of page
Flywheel cracking
bulletin October 5, 2006
While working on a friend's Honda engine the other day
I noticed a crack developing in the flywheel at the inner end of the
hub
and extending toward the web area. The crack starts at the trailing
corner
of the keyway.
The crack is not noticeable until a penetrant is applied and the
surface
wiped clean. Then the crack can be seen as the remaining penetrant
oozes
out of the crack. I noticed the crack when I was cleaning the
bore
area with "Brake Cleaner". The crack became visible when I wiped off
the
surplus Brake Cleaner. You can get a Dye Penetrant kit which will
do a better job of detecting cracks. After seeing the first crack I
checked
my engine and it had one too, in the same location. I suspect the cause
may be due to the high torque I use on the flywheel nut to keep it from
slipping on the crankshaft at high speed.
In an attempt to eliminate the chance of future
cracking, I have ground a small dimple to radius the corners of the
keyway
to about 0.20" in from the inside end of the keyway using a die
grinder.
This is done on a good flywheel that does not have a crack (a cracked
flywheel
cannot be repaired), I'm hoping that by removing the sharp corner of
the
keyway at its end I will relieve the "stress raiser" effect enough to
prevent
a crack from starting.
For an older version of this page with reference to Honda engines, click here.